Light-metal-casting alloy



UNITED TE PATENTD Patented Sept; '8, 1925.

, 1,553,298 FFICE.

mimic,- BunnIcx, or MIDLAND, MICHIGAN, AssIcNon Toms now CHEMICAL comm, or MIDLAND, women, a conronsrron or women.

' LIGnr-IIErAL-oAsrIno ALLOY.

11' 9 Drawing.

' To aZZ w libm it may concern:-

Be 'it known that I, EDWARD C; BURDICK,

a citizen of the United States, and a resident of Midland, county of Midland, and

1 State of Michigan, have invented anew and useful Improvement in Light-Metal-Casting Alloys, of which the following is;a specification, the principle of the invention being herein explained and the best mode in which I have contemplated applying that principle, so as to distinguish it from other in- I vention The present improvements relate more particularly to an alloy in .which the metal magnesium largely predominates, in contradistinction to hitherto commercially feasible light metal alloys, in which aluminum has uniformly been the predominant metal.

Thus while magnesium has been utilized in combination with aluminum to form the alloy magnalium, all authorities agree that no valuable alloy is produced where the proportion of magnesium exceeds ten per cent, and ordinarily only from one to two per cent of magnesium-is utilized in the alloy just referred to. 1

I have discovered that, contrary to the prevailing understanding, it is possible to I 1 produce an alloy of magnesium with alumiso" num, wherein the former constitutes upwards of ninety per cent of the total mass,

.which alloy possesses properties admirably the tensile strength.

adapting it for casting internal combustion motor pistons and'other like articles, which require the qualities of lightness, rigidity, and a yield point that is relatively high to 1 it the same time the alloy which I have obtained is superior for machining, taking a smooth finish at high f speeds, without rapid wear of tools, or tearmg or pulling along edge of cut. Furthermore, my Improved alloy is apparently usable directly ,without heattreatment, the objectionable tendencyto grow, characteristic of,so-ca ed aluminum alloys such as it has heretofore been attempted to use in conditions hereinafter fully'set forth andparticularly pointed out in-the claims, the

casting pistons, being so small as to be practically non-existent.

. In the production of'my improved alloy I employ the ingredients and observe the following description setting forth but one of the several ways in which the principle of the invention may be embodled.

Application .filed July 12, 1919. seriarm'. 1 ,436.

As a result of investigation and experiment, I have found that alloys high in magnesium'which, upon cooling, solidify without the formation of a eutectic, lack the rlgidity that is not only desirable but necessary 1n a cast article such as an internal combustion motor piston. In other words,

such article will crush under too light a load, and its yield point is relatively low.

It is necessary accordingly to add a sum-- cient quantity of the alloying metal to' produce a eutectic, but here again,'.'where the conditions to be met by the cast article when 1n use involve subjection to a considerable temperature, as in the example of the piston, just referred to, I have found that zinc and other alloy metals which it has heretofore been proposed to use, produce a eutectic of so low a melting point that the composite structure still lacks necessary rigidity and tensile strength. j i Y I have found that a. certain limited proportion of aluminum, when added to a predominating quantity 'of magnesium, goes into solid solution in such magnesium when the mass cools, so thatno appreciable eutectic is formed unless upwards of six per cent of aluminum is added. The addition of a further quantit of aluminum, then, will produce a eutectic, andif the amount of such eutectic be not too large the result,-

of crystals of solid saturated aluminummagnesium solution, embedded in and individually more or less surrounded by such eutectic, will possess all of the desired qualiam composite structure, consisting of a mass ties of rigidity, yield point, tensile strength,

and workability, specified above. Such alloy will of course be much lighter than one in which aluminum predominates, to a degree corresponding with the relative specific gravities of the two metals.

The most satisfactory proportions of the two metals I have found to be 91.5 per cent of magnesium, and 8.5 per cent of aluminum. Assuming that approximately six per cent of the aluminum goes into the saturated solid solution of the two metals, there is left togo into the eutectic the remaining 2.5 per, cent of such metal. "I have found that tracesmeasured in tenths of one per centof silicon or of silicon and iron, are of value as apparently additionally contributing to the qualities referred to above. An alloy of the abovecomposition, when cast,

- ing complete protection against further ac- V extent in the case .of the faniilar aluminum tion of this sort, while such oxide in the case of the alloy in hand in non-abrasive, which further distinguishes it from; the oxide that is formed 'in the case of such aluminum alloys.

In the case of castings made of the two metals in approximately the proportions indicated above, 'thestructure is found to undergo no appreciable transformation due to alternate heating andcooling, such as internal combustion motor pistons are sub-- jected to. As a result, the objectionable tendency to grow, which is present even in cast iron pistons, and to an annoying alloys, is eliminated. -'l.he euteoticformed ,in the case of an'alloy composed of magnesium and aluminum in the proportions stated melts at about 830 degrees F., so that a casting made of such will readily stand. temperatures from 700 degrees F. to 800 degrees F. witliout being alfected.

In order to prepare-the alloy, themagnesiumis first fused in a suitable crucible with a suitable salt flux covering same, and then the measured or wei hed amount of aluminum added thereto in the form of small pieces of the solid metal, the mass being thoroughly mixed as such pieces interfuse with the magnesium. The alloy begins to solidify at approximately 1130 degrees F, and while for sand casting it has been found desirable to raise the temperature to from 1200 to 1300 degrees F., a temperature under I 1200 degrees is satisfactory for die casting.

The flux used to coat the molten metal in the crucible should not be allowed to mingle with. the metal. that enters the mold in order that the casting may be free from occluded-salt or other like impurities.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the composition and structure herein disclosed, providing the ingredients or elementsof structure stated by any of the following claims or their equivalents be emp'loyed. o

I therefore point out and distinctly claim as my mventionz- 1. As a new product, a light metal alloy containing not less than 80 per cent and not more than 99.5 percent of magnesium, to-

messes gether with a trace, measured in tenths of one per cent of iron.-

2. As a new product, a light metal alloy containing not less than 80 per cent and not more than 99.5 per cent of magnesium, together with a trace, measured in tenths of one per centof silicon.

3. As a new product, a lightmetal alloy' containing not less than 80 per cent and not more than 99.5 per cent of magnesium, together with traces, measured in tenths of one per cent of iron and silicon.

l. As a new product, a light metal alloy containing magnesium and aluminum wherein the former metal largely predominates,

together with a trace, measured tenths of one per cent of iron.

1 5. As a new product, a light metal alloy containing magnesium and aluminum wherein the former metal largely predominates, together with a trace, measured in tenths of one per cent of silicon. v

6. As a new product, a light'metal alloy containing magnesium and aluminum wherein the former metal largely predominates, together with traces, measured in tenths of one per cent of iron and silicon.

7 As a new article of manufacture, a casting made of an alloy of magnesium with aluminum, the latter being present in a quantity not greatly in excess'of that re-' quired to form a saturated solid .solution with the magnesium, and the crystals of such saturatedsolid aluminum-magnesium solution being uniformly distributed through- .out the mass and embedded in a network of magnesium-aluminumeutectio so as to produce a finely grained structure.

. 8. As a new article of manufacture, a

casting made of an alloy of magnesium with ,aluminum, the latter constituting approximately eight and one-half per cent of the total, so as to produce asaturated solid solution with the magnesium with a small exsuch saturatedsolidaluminum magnesiumso I f cess of aluminum over, and the crystals of lution being uniformly distributed throughout the mass and. embedded in a net-work of magnesium-aluminum eutectic so' as to pro duce a finely grained structure. I 9.. As a new artlcle. of manufacture, a

casting made of an alloy of magnesium with aluminum, the latter' being present in a 1 quantity not greatly ,in excess of that required to form a saturated solid solution with the magnesium and the crystals of such saturatedsolid aluminum-magnesium solution being uniformly'distributed through out the mass and embed'ded in a net-work of magnesmm-alummum eutectic so as to pro duce a finely grained structure, the casting being substantially free from occluded salt or other like impurities. 4

10.;As a new article of manufacture,- a.

casting made of an alloy of magnesium with aluminum, the latter constituting approximately eight and one-half per cent of the solid Solution with the magnesium with a small excess of aluminum over, and the crystals of such saturated solid aluminummagnesium solution being uniformly distributed'throughout the mass and embedded in a net-work of magnesium-aluminum eutectic so as to produce a finely grained structure.

11. As a new article of manufacture, a casting made of an alloy of magnesium with aluminum, the latter constituting approximately eight and one-half per cent of the total, and with minimum measurable percentage of iron and silicon so as to produce a saturated solid solution with the magnesium with a small excess of aluminum over, and the crystals of such saturated solid aluminum magnesium solution being uniformly distributed throughout the mass and embedded in a net-work of magnesiumaluminum eutectic so as to produce a finely grained structure.

12. As a new article of manufacture, an internal combustion motor piston casting made of an alloy consisting predominantly of magnesium and containing aluminum in quantity only sufiicient to produce a limited amount of eutectic, such aluminum forming with the magnesium a eutectic having a' melting point above 7 00 F.,. said alloy also containing a trace of iron.

13. As a new article of manufacture, an internal combustion. motor piston casting made of an alloy consisting predominantly of magnesium and containing aluminum in quantity only sufiicient to produce a limited amount of eutectic, such aluminum forming with the magnesium a eutectic having a melting point above 700 F said alloy also containing traces of iron and silicon.

Signed by me, this 9th day of July, 1919.

EDWARD C. BURDIQK. 

